Electric heating device



' Nov. 10, 1936.

A. W. MULLER ELECTRIC HEATING DEVICE Filed Feb. 27, 1935 2 Sheets-Sheet1 I 74 f 5 I k9 \C I O 44 /0 I2 C) L o o 0 44 INVENTOR ATTORNEYS NOV.10, 1936. w MULLER 2,060,237

ELECTRIC HEATING DEVICE Filed Feb. 2'7, 1935 2 Sheets-Sheet. 2

INVENTOR raw ATTORNEYS Patented Nov. 10, 1936 UNITED STATES PATENTOFFICE 8 Claims.

This invention relates to portable electric heating devices such as areused for heating a small quantity of liquid in a test tube.

In making a so-called Benedict test of the urine of a diabetic person, asmall quantity of the urine is placed in a test tube containing Benedictsolution and the test tube is then heated. The heating is usuallyaccomplished by immersing the test tube in boiling water or holding itover an open flame. So far as I am aware there is no satisfactoryelectrical heating device available for this purpose. Heating devicesheretofore proposed for heating the contents of a test tube have been sodesigned that, if used for the Benedict test, the heat would not beapplied where needed, or else the heat would be so intensively appliedto, and concentrated at, the small quantity of liquid in the lower partof the test tube as to eject it by what is known as geyser action.Physicians and surgeons usually employ a gas burner to heat the testtube in making the Benedict test. This is a laboratory instrument andlacks the appearance of a finished product and is reluctantly used forwant of a better article. If the patient is making the test in his ownhome it 25 must be made where the open flame or the boiling water isavailable and he is therefore usually prevented from making the testwith the desired amount of privacy.

Among the objects of the invention are:

To provide an electric heating device which is especially suitable foruse in making a urine Benedict test;

To provide an electric heating device for heating a small quantity ofliquid in a test tube, or the like, in which the source of heat is solocated with respect to the test tube and its contents, and the heat isso controlled by certain provisions for insuring a proper circulation ofair, that the liquid will be properly heated without causing geyseraction in the liquid;

To provide a heating device which will constitute a neat and presentablefinished instrument for use in physicians offices;

To benefit diabetic patients by making available to them a satisfactoryelectric heating device which will eliminate the burdensome procedure inmaking Benedict tests, and which, due to its convenience and the privacyallowed, will cause the patient to check his condition oftener;

To provide a heating device which is compact and all of whose parts areenclosab-le in a casing to form a small unit capable of being easilycarried and transported in a suit case, or the like, so that Benedicttests may be made outside of ones home, and so that physicians may carryit with them in making visits to patients;

To enclose all of the working parts in an insulated casing to preventburning of the hands.

Other objects will hereinafter appear. 5.

The preferred embodiment of the invention is illustrated in theaccompanying drawings, in

which Fig. 1 is a perspective view of the device as it appears when thecover is in position; 10

Fig. 2 is a similar perspective View with the cover removed and a partof the side wall of the casing broken away to expose the interior parts;

Fig. 3 is a detailed perspective view of the dielectric base whichsupports the heating ele- 15 ment, the test tube, and other parts of thedevice, certain parts being shown in section to better illustrate itsconstruction;

Fig. 4 .is a transverse vertical section through the complete devicetaken on the line 4-4 of Fig. 5;

Fig. 5 is a horizontal section taken on the line 55 of Fig. 4;

Fig. 6 is a vertical transverse section of the complete device taken onthe line 66 of Fig. 4;

Fig. '7 is a vertical transverse section of the device with the coverremoved, the section being taken on the line 'l'l of Fig. 4; and

Fig. 8 is a horizontal section taken on the line 8-8 of Fig. 4.

When the cover of the heating device is in position, as shown in Fig. l,the exterior shape is that of a rectangular parallelepiped all of whosefaces are smooth and unbroken, except for a base l, an electric switch 2and a small lens 5 or crystal 3 whose functions will be hereinafterdescribed. The casing which receives the interior parts is shown at 4and the removable cover at 5. Secured to the metal base I by bolts 6 isa dielectric base 1, shown in its entirety in Fig. 3. 40

The lowermost part 8 of the dielectric base is rectangular in horizontalcross section and fits snugly within the lower portion of the casing 4,to which it is secured by horizontally positioned bolts 9. At one sideof the lower portion 8 of the base and rising vertically therefrom is ablock Ill to support certain elements hereinafter described. To one sideof the block in and rising vertically from the lower portion 8 are fourprojections ll, each of which, in horizontal cross section, has theshapeof a segment of a circle. The projections H are spaced apartcircumferentially. The innermost ends of the projections II do not meetbut are shaped so that the inner vertical faces form a central verticalopening 15 over the dielectric ring l4.

as shown at I 2 (Figs. 3 and A cylindrical sleeve l3 rises verticallyfor a short distance from the outer edges of the segmental projectionsII. A dielectric ring l4 mounted on or preferably 5 integral with thesegmental projections ll supports the heating element. The heatingelement comprises a resistor preferably formed by a conductor wound on amica strip, the entire resistor being designated by the numeral l5. Theresistor is enclosedin'a hollow sheet metal ring l6 closed at its topedge as shown at l1. The outer vertical wall of the sheet metal ring I6extends vertically downward below the inner wall as shown at I3 and isdesigned to telescope snugly The lower edge of the outer wall of themetal ring is crimped under the dielectric ring I4 at the spaces betweenthe segmental projections H as shown at I9 (Fig. 4). In this way, theheating element is firmly attached to the dielectric ring l4 and theresistor is completely enclosed at the sides and at the top by the metalof the ring and at the bottom by the upper surface of the dielectricring I4.

Telescoping within the upper end of the casing 4 is a sheet meta-lmember 20 which is secured to the walls of the casing by screws 2|. Thevertical walls of the member 20 form a neck portion over which the cover5 telescopes. The member 20 is closed at its top by a horizontal 'wall22, provided with a circular opening 23. A

40 upper end of the test tube projects beyond the top wall 22 of themember 20. When the cover 5 is in place a body of soft material, such assponge rubber 21 within the cover presses against the upper edge of thetest tube and holds it firmly 15 in position. An insulating sleeve 28 issupported within the upstanding ring [3 of the dielectric base andsurrounds the test tube, the sheet metal sleeve 24, and the heatingelement so as to prevent the outside casingfrom getting too warm 50' andto lessen the danger of burning the hands when handling the device.

The supply of current to the heating element is controlled by the switch2. A pilot lamp 29 whose light is visible through the lens 3 (Fig. 1)

55 indicates when the device is functioning as it is illuminated whencurrent is being supplied to the heating element and is out when nocurrent is being supplied to the heating element. The

. switch 2 and the lamp 29 are supported on the 60 upstanding block ll]of dielectric base.

Metal strips 30 and 3| serving as supports and also as conductors forthe switch are secured to the dielectric base by bolts 32 and 33. Theinnermost metal strip 3| is bent at its lower portion 65 to extend underand make contact with the lamp socket 34. A third bolt passes upwardlythrough the dielectric base and its head clamps the lamp socket 34 tothe block II]. The head of this bolt also serves as the central contact70 for the lamp socket. For this purpose the head of the bolt isinsulated from the lamp socket and from the metal strip 3| by aninsulating washer 36. One of the incoming leads, for instance, thatshown at 31 (Fig. 8) is connected to the lower 75 end of the bolt 35 andthe other incoming lead 38 is connected to the lower end of the bolt 32.One of the leads 39 from the resistor is connected to the lower end ofthe middle bolt 33 and the other lead 40 from the resistor is connectedto the lower end of the bolt 35. In this way the resistor and the pilotlamp are connected in parallel and both of them are controlled by theswitch 2. The bottom of the dielectric base may be recessed as shown at4| to accommodate the electric wires and to provide space for the nutsat the lower end of the bolts.

When the device is functioning heat passes upwardly from the resistorand is confined within the insulating sleeve 28 until it reaches the topof the sleeve where it is discharged to the outside atmosphere throughopenings 42 provided in the flaring upper end of the guide sleeve 24.

Any heat developed by the lamp 29 is discharged through openings 43 inthe insulating sleeve 28 near its upper end and then through theopenings 42 to the outside atmosphere.

The test tube, the guide tube 24, the heating element, the ring I4 onwhich it is mounted and the segmental projections l i are all socorrelated as to size and relative positions that when the test tube isresting on the seat formed by the inner circular edges at the top of thesegmental projections l I, no part of the heating element will makedirect contact with the test tube. The walls of the heating element andthe test tube are spaced radially apart as clearly shown in Fig. 4.Likewise, the ring l4 which supports the heating element is spacedradially away from the walls of the test tube. The amount of surfacecontact between the support and the test tube is very small because thetest tube rests on the circular line-contact seat formed by the edges ofthe projections II. This circular seat causes the test tube always torest exactly in the center so that it does not contact with the ring l4or the heating element or any metal part heated thereby.

Air is permitted to flow upwardly through the ring l4 and through thespace between the test tube and the inner wall of the heating element.Free access of air for this purpose is permitted by openings 44 in thelower portion 8 of the dielectric base. Eachof these openings is locatedbetween two of the segmental projections II as clearly shown in Fig. 3.The sheet metal base I is likewise provided with openings 45 to allowoutside air to enter the recess 4| in the bottom of the dielectric baseand then to pass upwardly through the openings 44, then between thesegmental projections H and then upwardly around the heating element.

It will be noted that the heating element is located near the bottom ofthe test tube, and as it surrounds the test tube the heat isconcentrated on the sides of the test tube for a limited distance. Whilethe heating element does not make contact with the test tube, it isplaced in close enough proximity to permit a full application of heat tothe test tube contents. No heat whatever is focused to the bottom of thetest tube. In fact the bottom of the test tube is cooled by a constantstream of air flowing upwardly to the heating element between theprojections II and through the central opening formed by the inner ends01' these projections. By placing the heating element near the lowerportion of the test tube, but not under it, by eliminating directcontact between the heating element and the test tube, and by admittingoutside air to the device and allowing it to impinge against the bottomof the test tube and to flow upwardly around the heating element and thetest tube it is possible to apply the right amount of heat to a smallquantity of liquid in the test tube without danger of ejecting thecontents of the test tube by geyser action. The device is thereforeparticularly useful in making a Benedict test.

The upper end of the test tube is preferably provided with a rubber ring46 which enables it to be handled while it is hot. This ring ispreferably made hexagonal or octagonal in shape so that the test tubewill not roll when lying in a horizontal position. The rubber ring alsoprevents breakage of the tube in case it should fall from a verticalposition upon its side.

In using the device it is only necessary to remove the cover 5, placethe test tube with its liquid contents in the guide tube 24 until thebottom of the test tube rests upon the upper inner edges of thesegmental projections H. The switch 2 is then operated to supply currentto the heating element l6. When the heating element is functioning thepilot lamp 29 will be illuminated and its light will be visible throughthe crystal or lens 3. Heat from the heating element will be sumciently,but not too severely, applied to the contents of the tube by radiation.The incoming air will cool the bottom of the test tube and will thenpass upwardly around the heating element and through the space betweenthe heating element and the test tube. It thus acts as a ventilatingmedium to prevent such an intense application of the heat as mightresult in geyser action. The air heated by the heating element continuesto flow upwardly to heat the upper portion of the test tube and is thendischarged through the openings 42.

It will now be seen that the device is compact and neat in appearanceand is the kind of an instrument which a physician does not object touse in his ofllce. When the cover is in place all parts are enclosed andthe test tube is held firmly in position and the device may be readilytransported. It may be used any place where electric current isavailable.

While my improved heating device was especially designed for use inmaking a Benedict test, and while its. advantages for this particularuse have been emphasized, it may, of course, be used for other purposes.

The foregoing description has been made specific because of itsreference to the preferred form of the invention, but that fact shouldnot be construed as an intention to limit the invention to theparticular form of the device described. On the contrary, many changescan be made, including variations in materials, dimensions, location ofthe parts, etc. without departing from the scope of the invention asdefined by the accompanying claims.

I claim:-

1. A heating device for heating the contents of test tubes, and thelike, comprising a base provided with circumferentially spaced verticalprojections upon which the test tube is adapted to rest, the base havingopenings located between said projections to permit air to flow upwardlyaround the test tube, and an annular electric heating element supportedby said projections and adapted to surround the test tube and having aninner diameter greater than the outside. diameter of the test tubewhereby air may flow upwardly through said openings then between theprojections and through the space between the heating element and thewalls of the test tube.

2. A heating device in accordance with claim 1 in which a sleevesupported by the outer ends of the projections surrounds the heatingelement and is spaced radially therefrom, and an insulating sleevetelescoping within the first named sleeve and surrounding the test tube.and the heating element.

3. A heating device comprising an outer casing, means in the lower partof the casing for supporting a receptacle, a guide for holding thereceptacle in an upright position, electric heating means surroundingthe receptacle, and a single cover for the casing adapted to enclose thetop of the casing and to seal the top of the receptacle.

4. A heating device comprising an outer casing, a receptacle support inthe lower part of the casing, an electric heating element surroundingthe receptacle, a member telescoping partl within the upper portion ofthe casing and having a top wall provided with an opening, said memberconstituting a neck portion for the casing, a receptacle guide securedto the top wall of said member at said opening and extending downwardlyinto the casing, and a cover for the casing adapted to be applied tosaid neck portion.

5. A heating device in accordance with claim 4 in which the receptaclewhen resting on the support projects above the top wall of said memberthrough its opening whereby it may be engaged by the end of the cover tosteady it when the member is in place.

6. An electric heating device comprising a casing having a top wallprovided with an opening, a receptacle guide extending into the casingand having a flared upper end joining the top wall of the casing at saidopening, a receptacle sup port below said guide, and an electric heatingelement adapted to surround the receptacle, the flared portion of saidguide having openings to permit the escape of heat from the casing.

7. An electric heating device comprising a casing, a receptacle supporttherein, an electric heating element within the casing to heat areceptacle and its contents, a cover for the casing and a body of softmaterial located at the inner side of the top wall of said cover forengaging the upper end of a receptacle when the latter is resting uponthe said support.

8. A heating device comprising a base having vertical projections whichare arranged to support a receptacle and spaced apart circumferentially,in circular arrangement, to provide air passages, said base havingopenings to admit air to the passages between said projections, wherebyair may flow through said passages upwardly around the receptacle, anelectrical heating means for heating said receptacle, said heating meanscomprising an annular heating element which surrounds a portion of thereceptacle but is spaced radially therefrom.

' ALFRED W. MULLER.

